Comet Catalina C/2013 US10 is currently visible in the Northern Hemisphere using binoculars or a small telescope. After rounding the Sun late in November, it has been up in the pre-dawn sky, creeping up higher each night.

It was observable in early December in New England, but very low in the sky before sunrise. I tried to get a look at it a few times using binoculars but was not able to see it well between the trees at home! Had hoped to see it later in December, but skies have been very cloudy and foggy for the past few weeks as part of a very unusually mild and damp weather pattern.

Having some time off recently, I thought I would try to see the comet using one of the internet telescope services available, and was able to get some images of it after signing up for a trial on slooh.com

After logging in and watching some of the getting started videos, I was able to book a timeslot (or “mission” as they call it) to see the Catalina comet on one of their telescopes in the Canary Islands . The site has a page titled “What’s Up” that gives a lot of great suggestions for currently observable objects to look at including planets, deep sky objects and visible comets. You simply select an available time, select the desired object you’d like to see and you are all set!

But for comets and other moving objects you need to determine the coordinates the target will be at and create a “Coordinate Mission” for that location of the sky. I used Stellarium to determine where Comet Catalina would be from the observatory location at the time of the reservation. Since the reservation times are in UTC, it is also handy to set the TimeZone plugin in Stellarium to work in that time zone. That way, you can check the position at a given time in UTC and not have to convert to your local time. (Or I guess you can change your workstation to UTC time and keep it there)! The coordinates calculated in Stellarium can be a bit off, so to get accurate positions expected from the coordinates of the actual observatory it’s good to use the MPC Minor Plan and Comet Ephemeris Service or the JPL Horizons site.

After you enter the coordinates, you select the type of object you are observing, so I selected the “bright comet” option. Apparently this setting determines the exposure time and image processing used for the session. The site appears to confirm that the coordinates are observable at the time selected and will even warn you if a fainter object is too close to the moon to be seen.

Once you set this all up, that’s it! You can stay on and watch the images from the telescope as they are taken. Since my reservation was around 1 AM local time, I just went to sleep while my images were being acquired!

The next day, I signed back into the site, selected the My Images page and found 4 images taken of the comet. The session used both a high magnification telescope (17″ CDK af f7) and a wide field APO refractor telescope. Images were taken at the same time, processed and made available as color and mono PNG files in the size of the original CCD images. These can be viewed on the site, downloaded, or annotated and emailed or shared to your favorite social media site.

Here is the high magnification image of C/2013 US 10 Catalina from this session on 30 Dec 2015:

It’s hard to see in the above version, but there is a faint tail extending up and right – I believe this is the dust tail. The ion tail extends a short ways down from the comet center. (North is up in this image).

I noticed several fuzzy objects around the comet. Not more comets, but apparently Catalina US10 was passing through an area with a few galaxies.

Slooh also provides FITS files from the CCD cameras. These are downloaded from the observatory at the end of each night and made available through the Slooh website and as well as an email notification.

So I was able to take the FITS file of the unfiltered or luminance image and reduce in Astrometrica. Then I could take estimated coordinates of each of the galaxies visible in the picture and check them against positions in TheSky. In the image above there are 5 clearly visible. I marked these in Astrometrica and they are shown in the image below, along with the fit and estimated location of the comets:

The dual tails are more clearly visible in the inverted image. I could also try stacking the color and luminance FITS files to see if I could bring these out better in the positive image. But I kind of prefer the above as it reminds me of working with AgBr imaging!

I took an image of the comet on the next night, and recently tried combining the FITS files to make my own LRGB composite using MaximDL. I need to better understand how to bring out the tails in that package but got a fairly good result:

The dust trail to the upper right appears to have a fork in it at this time – taken on 31 December.

The Catalina comet will continue to be visible through January and then fade as it moves away from the sun. Turns out this comet will not be back to greet us but will continue on outside of the solar system for parts unknown. Apparently is was a deep solar object that had its orbit perturbed enough to be knocked into an ejection trajectory that will take it outside of the Solar System.

Next, I will try capturing some of the other comets in the sky using Slooh and perhaps another similar service.